591
FXUS61 KPHI 221327
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
927 AM EDT Sun Jun 22 2025
.SYNOPSIS...
Hot high pressure across the western Atlantic will build west
into the Appalachian region early this week. This will result
in a significant heat wave with near record breaking temperatures
forecast. The high pressure system will begin to weaken and
retreat to the south by the middle to end of the week, and
temperatures will return closer to average along with increasing
chances for showers and thunderstorms as we get into next weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
A multi-day dangerous heat event begins today.
As of 925 AM, the leading edge of an MCS to our north continues
to settle southward and is now into our far northern zones. Some
lightning is also occurring. The main instability is sitting to
our north and west, however the flow setup is feeding this
instability into the convection as it continues to develop into
central New York State along its outflow. Increased the PoPs
quite a bit across the far northern areas given radar trends.
Also earlier increased the cloud cover quite a bit given the
clouds associated with this MCS crossing much of our area. These
clouds have thinned some over the last hour or so across the
portions of the region though. Hourly temperatures needed to be
adjusted as well especially across the north due to thicker
cloud cover and in some places some showers/thunder. We will
have to wait and see how this all impacts the temperatures/heat
indices going forward today.
Otherwise, the center of a strong upper-level ridge positioned
across the Ohio and Tennessee Valleys will expand northeastward
today. As this occurs, surface high pressure will build westward
from the far western Atlantic. This will all direct a hotter
and more humid air mass across our area through Sunday night.
A shortwave trough is currently sliding across New England this
morning. Shortwave energy along with some convectively enhanced
energy will drive one or more convection clusters around the
northern periphery of the building ridge. Some concern that
this line has plowed through upstate New York this morning,
producing widespread damage. There are signals in some of the
guidance as the convection moves across parts of New England
that a trailing outflow may settle into portions of our region
from the north. There is a low potential that some renewed
convection occurs along this lingering boundary farther south
during the day today, so an area of 15-20% PoPs were added for
northern Delaware into South Jersey and points north to blend
in with even the higher PoPs across the far north. Very low
confidence though on how this all plays out as much of the CAM
guidance is dry, but also struggle with decaying MCS`s and
outflow boundaries of those systems.
We will need to watch this potential though and also if some
storms can initiate over the terrain in the Pocono region or
this line over New York maintains strength as it moves in from
the north. If that happens, a strong or severe thunderstorm
cannot be ruled out especially with all the moisture and
instability present over the area. Most of the area is in a
MARGINAL (1/5) risk for severe and SPC added a SLIGHT (2/5) risk
north of I-78. This is a VERY conditional threat and most areas
will see nothing at all other than hot and humid conditions.
Would describe this as a low floor, moderate to high ceiling
event. Also worth noting that northwest flow systems tend to
over-perform, as this line moving through upstate NY has proven
yet again.
Today is the start of a multi-day dangerous heat event, with
high temperatures rising into the mid 90s (some upper 90s)
across much of the area. The dew points will also increase into
the upper 60s to low 70s, although these could mix out a little
during peak heating especially across the coastal plain. Heat
indices to around 100 degrees are expected for nearly the entire
region, with these a little lower in the higher elevations and
closest to the coast. As a result, the Extreme Heat Warning and
Heat Advisory both begin this morning. For far southern New
Jersey and most of our Delmarva zones, the criteria here is
higher and therefore continued to not include them in a heat
related headline for Sunday. A stronger breeze develops on
Sunday, although given ample heating over land the wind
direction may stay more southwest or south-southwest for the
coastal areas keeping the New Jersey beaches especially cooler
than a few miles inland.
It will be very warm and muggy Sunday night as dew points rise some
and low temperatures drop only into the 70s. It may struggle to drop
below 80 degrees in the highly urbanized centers.
&&
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Significant heat wave peaking Monday and Tuesday with
dangerously hot and humid conditions expected.
A strong ridge of high hot and dry pressure will build across
the eastern US Monday and Tuesday. Mid level heights,
thicknesses, and 850 mb temperatures contributing to the heat
wave will all peak during this time frame. The center of the
ridge will be positioned to our southwest, which should maximize
heat potential locally. At the surface, winds will be modest
from the west or northwest. This will add a component of
downsloping into the temperature equation, helping to boost
temperatures by a couple degrees. The wind direction will also
lessen the influence of the sea breeze, or lack thereof, for
coastal areas. The pattern is checking a lot of boxes for a set
up capable of producing fairly widespread 100 degree
temperatures in our region, perhaps one of the most favorable
patterns in a few years.
Fortunately, the pattern will favor dewpoints mixing out
reasonably well into the afternoon hours, but the high
temperatures will still result in heat indices of around 100-110
degrees across the board both Monday and Tuesday. At this
point, Monday looks to be the most humid of the 2 days, and thus
highest heat index day with heat indices around 105-110 degrees
in many areas. Slightly drier air, slightly stronger northwest
flow, and perhaps deeper mixing on Tuesday will favor slightly
higher temperatures, but heat indices should be near or perhaps
a few degrees lower than Monday. Regardless of those details,
it`s going to be very hot both days!
Extreme Heat Warnings and Heat Advisories remain in effect as
previously issued. Around the Delaware Valley, Lehigh Valley,
and northern New Jersey, temperatures could be the hottest
observed in over a decade. There will be little relief overnight
as temperatures Monday night and Tuesday Night are expected to
be around 75 to 80 degrees. Heat tends to have cumulative
effects on the body and we are currently forecasting 4
consecutive days of 95+ with Monday and Tuesday likely to
feature high temperatures around 100 degrees and heat index
values pushing 105-110 degrees. Take frequent breaks if outside,
and drink plenty of fluids. Not much else to say to highlight
the threat and main story of the upcoming week.
For details regarding the last 100 degree day and temperature
records during the upcoming heat wave, see the Climate section
below.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
For Wednesday and Thursday...The upper-level ridge weakens a
little bit and flattens out/erodes, especially on the northern
periphery. While the heat and humidity looks to continue, it
should decrease at least some by Wednesday, and especially
Thursday and Friday with continued erosion of the northern side
of the ridge. In addition, a surface trough should become better
defined and introduce a bit more clouds and also the potential
for at least some diurnally driven convection. There is a cold
front that tries to slide southward on Wednesday, but there is a
decent amount of uncertainty with how far south the cold front
makes it given the strength of the ridge. Due to this front,
there is a slight chance to chance (15-30%) of showers and
thunderstorms late Wednesday from the Philadelphia metro on
north and west. Increased cloud cover will keep temperatures a
touch cooler on Wednesday, but the Extreme Heat Warning remains
in for northern Delaware, the Philadelphia metro, Lehigh Valley,
and central/northern NJ. Temperatures will be a few degrees
cooler compared to Monday/Tuesday, but still in the mid to upper
90s, marking the 4th consecutive day of highs greater than 95
degrees. Heat indices will be near 100 degrees on Wednesday too,
so a slight improvement, but still hot.
As mentioned above, the ridge erodes a bit towards the end of
the week with a signal for some troughing building in from the
north that could lead to showers and thunderstorms both days to
end the week. The temperatures look to still hold near 90
degrees on Thursday and in the 80s by Friday, with heat indices
still in the 90s but this will be lower than earlier in the
week.
Unsettled weather looks to continue into the weekend with
temperatures even potentially dropping into below normal
territory.
&&
.AVIATION /13Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...VFR. Southwest winds increasing to 10-15 knots, with
some gusts to 20 knots this afternoon. Slight chance of a shower
or thunderstorm at all terminals in the afternoon. Low
confidence regarding the chance for convection.
Tonight...VFR. West-southwest winds 5 knots or less, becoming
more northwesterly late. Moderate confidence.
Outlook...
Monday through Tuesday Night...VFR. No significant weather.
Wednesday and Thursday...Prevailing VFR, though chances of a
shower/thunderstorm (20-40%) for the I-95 and Lehigh Valley
terminals, especially Thursday.
&&
.MARINE...
No marine headlines expected through tonight. Southwest winds
10-15 knots with seas 2 to 3 feet.
Outlook...
Monday through Thursday...No marine headlines expected.
Rip Currents...
For today, SW winds increase to 10 to 20 mph with breaking
waves of 2 to 3 feet. This will result in a MODERATE risk for
the development of dangerous rip currents for the Jersey Shore
counties of Ocean, Atlantic, and Cape May. For the Jersey Shore
county of Monmouth, as well as Delaware Beaches, flow will be a
bit more offshore, resulting in a LOW risk for the development
of dangerous rip currents.
For Monday, W to NW winds of 5 to 10 mph will turn S in the
afternoon behind developing sea breezes. Since winds will be
fairly light and breaking waves around 1 to 2 feet, there will
be a LOW risk for the development of dangerous and life
threatening rip currents for the Jersey Shore and for Delaware
Beaches.
For specific beach forecasts, visit weather.gov/beach/phi
&&
.TIDES/COASTAL FLOODING...
With the New Moon approaching on June 25th, astronomical tides
are expected to increase. Spotty minor tidal flooding is
anticipated for the immediate coastline and back bays as well as
within Delaware Bay beginning with the high tide on Monday
Night. Cannot rule out the need for advisories later this week
as astro tides peak. No tidal flooding is expected within the
tidal Delaware River or Chesapeake Bay.
&&
.CLIMATE...
Near record breaking heat is expected across the area through
the middle of next week. Below is a look at the last 100 degree
day, daily record high maximum and minimum temperature for all
of our climate sites.
Most Recent 100 Degree Day
Site Date/Temperature
Allentown (ABE) July 22, 2011/104
AC Airport (ACY) July 21, 2019/100
AC Marina (55N) July 5, 1999/101
Georgetown (GED) July 21, 2019/100
Mount Pocono (MPO) July 3, 1911/103
Philadelphia (PHL) July 18, 2012/100
Reading (RDG) June 22, 2024/101
Trenton (TTN) July 18, 2012/100
Wilmington (ILG) July 18, 2012/101
Record High Temperatures
June 23
Site Record/Year
Allentown (ABE) 96/2024
AC Airport (ACY) 98/1988 & 2024
AC Marina (55N) 91/1909
Georgetown (GED) 100/1988
Mount Pocono (MPO) 90/1954
Philadelphia (PHL) 98/2024
Reading (RDG) 98/2024
Trenton (TTN) 97/1894
Wilmington (ILG) 100/1894
Record Warmest Low Temperatures
June 23
Site Record/Year
Allentown (ABE) 71/2017 & 2024
AC Airport (ACY) 75/2024
AC Marina (55N) 74/2010
Georgetown (GED) 76/1988
Mount Pocono (MPO) 69/2024
Philadelphia (PHL) 76/1888
Reading (RDG) 77/2024
Trenton (TTN) 74/2017 & 2024
Wilmington (ILG) 75/2024
Record High Temperatures
June 24
Site Record/Year
Allentown (ABE) 98/1923
AC Airport (ACY) 99/2010
AC Marina (55N) 95/2002
Georgetown (GED) 97/2010
Mount Pocono (MPO) 92/1914
Philadelphia (PHL) 99/1923
Reading (RDG) 98/1908 & 1923
Trenton (TTN) 98/1894
Wilmington (ILG) 102/1894
Record Warmest Low Temperatures
June 24
Site Record/Year
Allentown (ABE) 71/2010
AC Airport (ACY) 72/1951, 2013, 2017 & 2024
AC Marina (55N) 72/1924, 2002, 2010, 2011, 2013 & 2020
Georgetown (GED) 74/2010
Mount Pocono (MPO) 66/1960, 1964 & 2002
Philadelphia (PHL) 75/1909, 1921, 1994 & 2020
Reading (RDG) 73/1909, 1994 & 2010
Trenton (TTN) 76/1894 & 2010
Wilmington (ILG) 74/1994
Record High Temperatures
June 25
Site Record/Year
Allentown (ABE) 98/1923
AC Airport (ACY) 96/1997
AC Marina (55N) 95/1952
Georgetown (GED) 96/1952
Mount Pocono (MPO) 91/1952
Philadelphia (PHL) 98/1952
Reading (RDG) 99/1943
Trenton (TTN) 99/1997
Wilmington (ILG) 98/1894
Record Warmest Low Temperatures
June 25
Site Record/Year
Allentown (ABE) 74/1923 & 1976
AC Airport (ACY) 80/1950
AC Marina (55N) 75/1997 & 2002
Georgetown (GED) 75/2019
Mount Pocono (MPO) 69/1952
Philadelphia (PHL) 76/1909, 1976 & 2002
Reading (RDG) 75/1943 & 1949
Trenton (TTN) 75/1976
Wilmington (ILG) 75/1976
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Extreme Heat Warning until 8 PM EDT Wednesday for PAZ060>062-
070-071-101>106.
Heat Advisory until 8 PM EDT Tuesday for PAZ054-055.
NJ...Extreme Heat Warning until 8 PM EDT Wednesday for NJZ001-
007>010-012-013-015-017>020-027.
Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for NJZ014-
016-021>026.
DE...Extreme Heat Warning until 8 PM EDT Wednesday for DEZ001.
Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for
DEZ002>004.
MD...Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for MDZ012-
015-019-020.
MARINE...None.
&&
$$
SYNOPSIS...Hoeflich/Staarmann
NEAR TERM...Gorse/Hoeflich
SHORT TERM...Hoeflich/Staarmann
LONG TERM...Hoeflich/Staarmann
AVIATION...Gorse/Hoeflich
MARINE...Hoeflich
TIDES/COASTAL FLOODING...Hoeflich
CLIMATE...Hoeflich/Staarmann